Fumaroles, hot springs, and mud pots line the trail through Bumpass Hell in Lassen Volcanic National Park. Named for early mountaineer Kendall Bumpass, who lost a leg after falling into a boiling mud pot, the area has one of the hottest hydrothermal fumaroles in the world. Big Boiler, the vent emitting the large steam cloud in the top left of the frame, has been measured at 327°F (164°C). Such otherworldly features are fueled by a residual mass of cooling magma about three miles below the Earths surface. Accompanied by gases such as hydrogen sulfide and sulfur dioxide, superheated groundwater rises to the surface. The vented acidic steam chemically transforms volcanic rock into clay, often tinted yellow, tan, or pink by iron hydroxides.